I. Field of the Invention
The present invention relates generally to a wireless communication system
and more particularly to a method and apparatus for reducing
a frame error rate FER (Frame Error Rate) in one
Wireless communication system.
II. Related Art
a wireless connection will be delivered, which is a relatively bad one
FER has (for example, more than 1%) many methods exist
data to achieve FER as low as the data service
calls. For example, a cyclic redundancy check (CRC
= cyclic redundancy check) at a receiving end of a connection
to check a data block. The
CRC is a well-known method to set up or determine
that data was received correctly in data communications. One
CRC character is generated at a sending device and becomes
attached to a data block.
The receiving end leads
Calculation and compares its results with the added CRC character.
If there is a difference, the receiving end requests the retransmission
of the data block.
may be the application of protocols, such as the automatic retransmission request
(ARQ = Automatic Retransmission reQuest) for retransmission
of data blocks
be used. In the ARQ, the sending device encodes
Error detection field (for example, a CRC field) based on the contents of a
Data block. The receiving end recalculates the check box
and compare it to what was received. If they match,
will be a confirmation
(ACK = acknowledgment) back
transmitted to the sending device.
If they do not match, a negative acknowledgment (NAK
= negative acknowledgment)
sent and the sending device retransmits the message.
The method discussed above is satisfactory for transmission
of many types of data. However, these methods cause
to achieve a low FER, increased latency due to retransmission
of data blocks.
Such increased latency is unacceptable when certain species
transmitted by data
be such as in real-time digitized language, or
any other type of latency-sensitive data. Especially
causes the retransmission
of data blocks
which are both higher on average
are, as well as a greater variance
have as the requirements for
Latency sensitive systems.
discloses a portable radio having an improved open-loop control scheme in which a transmitter power controller estimates the signal strength and signal quality of the downlink signal by determining a threshold set parameter for the received signal, eliminating a wrong power setting performed by the interfering signals are caused when RSSI (Received Signal Strength Level) is used as the means for estimating the transmitter power level. The threshold adjustment parameter is an adjustment parameter used in producing a degraded signal having a predetermined signal quality, and is determined by incrementally adjusting the received signal until it is determined that the degraded signal has the predetermined signal quality.
are a method and apparatus for providing data with
low FER without exhibiting increased latency. In other words,
there is a need for
a method and apparatus for reducing the FER, which
not on the retransmission
of data blocks
SUMMARY OF THE INVENTION
The present invention is directed to a method and an apparatus
directed to controlling a signal transmission power. The procedure
The present invention includes the steps of receiving
Signal to demodulate to produce a de modulated signal
and to distort the demodulated signal by a distorted demodulated signal
Generate signal. The demodulated signal may be, for example
be distorted by noise. A signal quality measurement, such as
a signal-to-noise ratio
(SNR), is then based on the distorted demodulated signal
rather than being determined based on the demodulated signal. A setting
the transmit power is then based on the signal quality measurement of the
Distorted demodulated signal requested.
In one embodiment of the present invention, the particular signal quality measurement is compared to a threshold, and then an adjustment of the transmit power based on the results of the comparison is requested. The threshold represents a desired minimum signal quality level at which signals should be received. Certain quality measurement functions, such as SNR, have values that are proportional to the signal quality. That is, they increase with increased quality and decrease with decreasing quality. Therefore, an increase in transmit power is requested when these signal quality measurements fall below the threshold, and a reduction in power may be requested when the signal quality measurements exceed the threshold. Other functions based on error events have values that are inversely proportional to signal quality and decrease in value with increased signal quality, and vice versa. In this situation, a reduction in transmission power is requested when the measurement falls below the threshold, and an increase in power is requested when the measurement exceeds the threshold.
the method of the present invention further comprises the steps of
to decode the demodulated signal to decision data
and decode the distorted demodulated signal to
create distorted decision data. A second signal quality measurement,
or a measurement of "error events" is then based
on the distorted decision data (and not based on the decision data)
certainly. The threshold used in determination of whether
to increase the transmission power or
is to be decreased based on the second signal quality measurement
where the signal is sent through a base station and from a user terminal
is received, the steps of the present invention by
the user terminal is running
and the transmission power at the base station is controlled.
a further embodiment,
where the signal is sent through a gateway or switchboard
and from a user terminal using a satellite
is received, the steps of the present invention by the
User terminal running
and the transmission power of the gateway is controlled.
yet another embodiment where
the signal is sent from a user terminal and from a user terminal
Base station, it is the transmission power at the user terminal,
which is controlled.
a further embodiment,
the signal is sent from a user terminal and from
receive a gateway or a switching point via a satellite
will be, the steps of the present invention through the gateway
and the transmission power of the user terminal is controlled.
BRIEF DESCRIPTION OF THE DRAWINGS
Features, objects and advantages of the present invention will become apparent
the detailed description set forth below is more apparent
when seen in conjunction with the drawings,
in which the same reference numerals everywhere
same or similar
Denote elements, and wherein the figures represent:
1 a typical communication system in which the present invention is useful;
2 an exemplary transceiver device for use in a user terminal;
3 an exemplary transmitting and receiving device for use in a gateway;
4A a block diagram of a power control scheme;
4B a block diagram of a power control scheme according to a preferred embodiment of the present invention;
5 FIG. 10 is a flowchart depicting the operation of an internal power control loop used by a power control determination element in one embodiment of the present invention; FIG.
6 FIG. 10 is a flowchart depicting the operation of an external power control loop used by a power control determination element in one embodiment of the present invention; FIG.
7 a flow chart depicting a high-level operation of a preferred embodiment of the present invention;
8A the SNR threshold over time for a user terminal which the power control scheme of 4A used; and
8B the SNR threshold over time for a user terminal which the power control scheme of 4B used.
THE PREFERRED EMBODIMENTS
The preferred embodiment of the invention will be discussed in detail below. While specific steps, configurations and arrangements are discussed, it should be understood that this is done for illustrative purposes only. Easy It will be appreciated that other steps, configurations and arrangements can be used without departing from the spirit and scope of the present invention.
I. Exemplary environment
the invention is described in detail, it is useful to exemplify
To describe environment in which the invention can be established.
The present invention can be used in many wireless communication systems
be set up, especially in one, which is the size of the transmission
control the power used for a signal. Such environments
indicate, without limitation,
cellular and terrestrial cellular telephone systems. A preferred
Application is in Code Division Multiple Access (CDMA) wireless spread spectrum communication systems
(Code Division Multiple Access) for mobile or portable telephone service.
The present invention is particularly applicable to communication systems
suitable to use the satellites in the low Earth orbit.
However, as will be apparent to those skilled in the art, the concept may be
of the present invention also to other types of satellite and
terrestrial communication systems.
Satellite-based communication systems use gateways and
one or more satellites to communicate signals between the
Forward gateways and one or more user terminals.
Gateways see communication links from each user terminal
connected to other user terminals or users of others
Communication systems, such as from a public
Telephone network. Typical terrestrial systems use base stations,
to send a signal and a signal from a user terminal
to recieve. The user terminals can be fixed or mobile
such as a mobile phone.
Some satellite-based and terrestrial communication systems employ Code Division Multiple Access (CDMA) spread spectrum signals, as described in U.S. Pat U.S. Patent No. 4,901,307
, issued February 13, 1990, entitled "Spread Spectrum Multiple Access Communication Systems Using Satellite or Terrestrial Repeaters," and US Pat U.S. Patent No. 5,691,974
, issued November 25, 1997, entitled "Method and Apparatus for Using Full Spectrum Transmitted Power in a Spread Spectrum Communication System for Tracking Individual Recipient Phase Time and Energy," both of which are assigned to the assignee of the present invention.
In a typical spread spectrum communication system, one or
Pseudo noise (PN) code sequences (PN = pseudonoise) are used to
Information signals about
to modulate or "spread" a predetermined spectral band, before the
Modulation on a carrier signal
as communication signals. PN code spreading, a method of spread spectrum transmission,
which is well known in the art generates a signal for transmission which
a much larger bandwidth
than that of the data signal has. In a base station or a gateway user communication connection, be
PN spreading codes or binary
Sequences used to distinguish between signals passing through
different base stations or gateways are sent, or via different beams,
as well as between multipath signals.
a typical CDMA spread spectrum system becomes channelization codes
used to distinguish between signals that are different
Users are provided in a cell, or between user signals,
those in a satellite sub-beam or forward link
(i.e., the signal path from the base station or
the gateway to the user terminal transceiver).
Each user transceiver (transceiver) has its own orthogonal channel,
the on the forward link
is provided by using a unique "channelizing" orthogonal code.
Signals transmitted on these channels
are commonly referred to as "traffic signals". Additional channels are for "paging", "synchronization" and other signals
intended to be sent to system users. Walsh functions
are generally used to set up the channelizing codes,
which are also known as Walsh codes.
CDMA spread spectrum,
as disclosed in the above patents, draw
Application of coherent modulation
and demodulation for
Forward link user terminal communications
into consideration. In communication systems that use this approach,
is a "pilot" or "Vorträgersignal", which is also referred to as "pilot signal",
as a coherent one
Phase reference for
the forward link signals
used. This means,
a signal containing no data modulation is passed through a gateway
or a base station via
transmit a coverage region for reference.
Pilot signals are used by the user terminals to obtain initial system synchronization and to time, frequency and phase track other signals seen by the gateway or base station. Phase information obtained from the tracking of a pilot signal is used as a carrier phase reference for coherent demodulation of other system signals or traffic (data) signals. This technique allows many traffic signals to use a common pilot signal as a phase reference, providing a more cost effective and efficient tracking mechanism. A single pilot signal is typically transmitted by each gateway or base station for each frequency used, also referred to as a CDMA channel or sub-beam, and used in common by all user terminals receiving signals from that gateway or base station at that frequency.
and base stations can
Information about user terminals using one or
provide several signals known as paging signals
are transmitted to paging channels
become. If, for example, a call to a special mobile phone
has been addressed, the gateway alerts the mobile phone
a paging signal. The paging signals are used to detect the presence
of a call, continue to use which traffic channel
is, and also for additional
System overhead information
together with for
distribute the user terminal to specific messages. One
Communication system can use multiple paging channels
to have. Synchronization signals can also
used to send system information that is useful
to enable a time synchronization. All these signals
act as shared resources in a similar manner to the pilot signals.
User terminals can
to a paging signaling message
respond by sending an access signal over a reverse link (i.e.
H. the signal path from the user terminal to the base station or the
Access signals are also used by the user terminals,
if they are the origin of calls.
in any communication system, the communication signals become
received by the user terminal and at a baseband frequency
converted down for further processing. As soon as she's downgraded
are the signals are processed digitally to the special pilot signal or
to detect the pilot signals that are received and associated
Demodulate paging, synchronization and traffic signals.
Demodulation, the PN spreading codes are applied to the signals
to despread and the channelization codes will be with the signals
correlates to deliver data.
An exemplary wireless communication system in which the present invention is useful is disclosed in U.S. Pat 1 illustrated. It is considered that this communication system uses CDMA-type communication signals, but this is not required for the present invention. In a part of an in 1 illustrated communication system 100 are a base station 112 , two satellites 116 and 118 and two associated gateways or hubs 120 and 122 shown to communicate with two remote user terminals 124 and 126 to effect. Typically, the base stations and satellite / gateways are components of separate communication systems, referred to as terrestrial and satellite based, although not necessary. The total number of base stations, gateways and satellites in such systems depends on the desired system capacity and other factors well known in the art.
The user terminals 124 and 126 each have or include a wireless communication device, such as, but not limited to, a cellular transceiver (transceiver) or a paging receiver, and may be in the hand or to be mounted on a vehicle if desired. In 1 is the user terminal 124 as a vehicle-mounted device, and the user terminal 126 is illustrated as a hand held mobile phone. It should also be understood, however, that the teachings of the invention are also applicable to fixed units where remote wireless service is desired. User terminals are sometimes also referred to as subscriber units, mobile stations, mobile units, or simply "users" or "subscribers" in some communication systems, depending on the preferences.
In general, rays from satellites cover 116 and 118 different geographic areas in predefined patterns. Beams at different frequencies, also referred to as CDMA channels or "sub-beams," can be routed to overlap the same region. It is also well known to those skilled in the art that beam coverage or service areas for multiple satellites or antenna patterns for multiple base stations could be designed to completely or partially overlap in a given region, depending on the communication system design and type of service offered, and whether a spatial diversity is achieved.
A variety of multi-satellite communication systems have been proposed an exemplary system of the order of 48 or more satellites running in eight different low earth orbit (LEO) orbital planes to service a large number of user terminals. However, one of ordinary skill in the art will readily understand how the teachings of the present invention are applicable to a variety of satellite system and gateway configurations, including other round trip distances and constellations. At the same time, the invention is also applicable to terrestrial based systems of various base station configurations.
In 1 There are some possible signal paths for communications that are shown between user terminals 124 and 126 and the base station 112 or by satellite 116 and 118 with gateways 120 and 122 are set up. The base station user terminal communication links are by lines 130 and 132 illustrated. The satellite user terminal communication links between the satellites 116 and 118 and the user terminals 124 and 126 are by lines 140 . 142 and 144 illustrated. The gateway satellite communication links between the gateways 120 and 122 and the satellite 116 and 118 are by lines 146 . 148 . 150 and 152 illustrated. These communication links can also be referred to as communication channels. The gateways 120 and 122 and the base station 112 can be used as part of one or two-way communication systems, or simply to send messages or data to the user terminals 124 and 126 , In a preferred embodiment, the gateways become 120 and 122 and the base station 112 used as part of a two-way communication system.
An exemplary transceiver or transceiver 200 for use in a user terminal 124 . 126 is in 2 illustrated. The transceiver 200 uses at least one antenna 210 for receiving communication signals to an analog receiver 214 where they are downsampled, amplified and digitized. A duplex element 212 can be used to allow the same antenna to serve both transmit and receive functions. However, some systems employ separate antennas for operation at different transmit and receive frequencies.
The digital communication signals coming from the analog receiver 214 output to at least one digital data receiver 216A and to at least one viewfinder receiver 218 Posted. Additional digital data receivers 216B - 216N can be used to achieve desired levels of signal diversity, depending on the acceptable level of user terminal complexity, as would be apparent to those skilled in the art in question. The digital data receivers 216A - 216N are used to despread and correlate the received signals addressed to the user terminal.
At least one user terminal control processor 220 is with the digital data receivers 216A - 216N and the viewfinder receiver 218 coupled. The control processor 220 provides, among other functions, basic signal processing, timing, power and handoff control or coordination, and the selection of a frequency used for signal carriers. Another basic control function, often by the control processor 220 is the selection or manipulation of PN code sequences or orthogonal functions to be used for processing communication signal waveforms. The signal processing by the control processor 220 may include a determination of the relative signal strength and a calculation of various related signal parameters. Calculations of signal parameters, such as timing and frequency, may include the use of additional or separate dedicated circuitry to provide increased efficiency or speed of measurements or improved allocation of control processing resources.
The outputs of the digital data receivers 216A - 216N are with a diversity combiner and decoder circuit 222 coupled in the user terminal. The digital data receivers 216A - 216N provide demodulated user data, such as digitized coded speech, to the diversity combiner and decoder circuit 222 , The diversity combiner and decoder circuit 222 combines the different signals from the digital data receivers 216A - 216N to provide a single user data signal. A user digital baseband circuit 224 also performs decoding and error correction on the user data.
The signal coming from the diversity combiner and decoder circuit 222 is output, becomes the digital baseband circuit 224 delivered to the user for interface transmission. The user digital baseband circuit 224 has processing and presentation elements that are used to transfer information to and away from a user terminal. That is, signal or data storage elements, such as a transient or long-term digital memory; Input and output devices, as in for example, display screens, speakers, keyboard terminals and headphones; A / D elements, vocoder and other speech and analog signal processing elements; etc. form all parts of the user terminal baseband circuit 224 using elements well known in the art. Some of these elements can also be under the control of the control processor 220 or work in conjunction with this.
When voice data or other data is prepared as an output message or an outgoing communication signal originating from the user terminal, the user digital baseband circuit is prepared 224 used to capture, store, process, and otherwise prepare for sending the desired data. The user digital baseband circuit 224 delivers this data to a transmit modulator 226 which is under the control of the control processor 220 is working. The output of the transmit modulator 226 becomes a power control device 228 which provides output power control for a transmit power amplifier 230 for the eventual transmission of the output signal from the antenna 210 to a gateway 120 . 122 or a base station 112 provides.
Information or data corresponding to one or more measured signal parameters for received communication signals or one or more shared resource signals may be sent to the gateway using a variety of techniques known in the art. For example, the information may be transmitted as a separate information signal or may be appended to other messages sent by the user digital baseband circuit 224 were prepared. Alternatively, the information may be transmitted as predetermined control bits by the transmit modulator 226 or the transmission power control device 228 under the control of the control processor 220 be inserted.
The digital receiver 216A - 216N and the viewfinder receiver 218 are with signal correlation elements bez. -correlators configured to demodulate and track specific signals. The viewfinder receiver 218 is used to search for pilot signals or for other relatively strong signals with relatively fixed patterns while the digital receiver 216A - 216N can be used to demodulate other signals associated with detected pilot signals. Therefore, the outputs of these units can be monitored to determine the energy in the pilot signals or other signals or their frequency. These receivers also employ frequency tracking elements that can be monitored to provide current frequency and timing information to the control processor 220 for just demodulated signals.
Additional details of the digital data receivers 216A - 216N , the diversity combiner and decoder circuit 222 and the digital baseband circuit 224 According to an embodiment of the present invention are described in the description below 4A and 4B discussed.
An exemplary transmitting and receiving device 300 for use in the gateways 120 and 122 is in 3 illustrated. The in 3 illustrated part of the gateway 120 . 122 has one or more analogue receivers 314 that with an antenna 310 are connected to receive communication signals which are then downconverted, amplified and digitized using various schemes well known in the art. Several antennas 310 are used in some communication systems. Digitized signals coming from the analogue receiver 314 are supplied as inputs to at least one digital receiver module, as indicated by dashed lines in general 324 shown.
Each digital receiver module 324 corresponds to signal processing elements used to communicate between a gateway 120 . 122 and a user terminal 124 . 126 although certain variations are known in the art. An analogue receiver 314 can inputs for many digital receiver modules 324 and a number of such modules will typically be in the gateways 120 . 122 used to record all satellite beams and possible diversity mode signals being handled at any given time. Each digital receiver module 324 has one or more digital data receivers 316 and a viewfinder receiver 318 , The viewfinder receiver 318 generally looks for suitable diversity modes of signals other than pilot signals. When set up in the communication system, multiple digital data receivers are created 316A - 316N used for diversity signal reception.
The outputs of the digital data receivers 316 become the following baseband processing elements 322 which have devices that are well known in the art and are not further illustrated in detail herein. An exemplary baseband device includes diversity combiners and decoders to combine multipath signals into one output for each user. An exemplary baseband device also includes interface circuits to provide output data, typically to a digital switch or network. A variety of however, their known elements, such as, but not limited to, vocoders, data modems, and digital data switching and memory components, may form part of the baseband processing elements 322 form. These elements operate to send data signals to one or more transmit modules 334 control or instruct.
Signals to the user terminals 124 . 126 are to be sent, each with one or more suitable transmission modules 334 coupled. A typical gateway 120 . 122 uses a number of such transmit modules 334 to provide a service for many user terminals 124 . 126 at the same time and for different satellites and beams at the same time. A base station 112 may also use a number of such modules, although the base stations tend to group transmit and receive functions closer together in modem structures. The number of transmit modules 334 coming from the gateway 120 . 122 is determined by factors known in the art, including the complexity of the system, the number of satellites being viewed, the system user capacity, the degree of diversity selected, and so forth.
Each transmission module 334 has a transmit modulator 326 on which modulates data for transmission by spread spectrum. The transmit modulator 326 has an output connected to a digital broadcasting power control device 328 which controls the transmit power used for the outgoing digital signal. The digital broadcasting power control device 328 applies a minimum level of performance for purposes of interference reduction and resource allocation, but applies appropriate power levels, if necessary, to compensate for attenuation in the transmission path or other path transmission characteristics. At least one PN generator 332 is done by the transmit modulator 326 used in spreading the signals: This code generation can also form a functional part of one or more control processors or memory elements in the gateway 120 . 122 be used.
The output of the transmission power control device 328 becomes an addition device 336 where it is summed with outputs from other transmit power control circuits. These outputs are signals for transmission to user terminals 124 . 126 with the same frequency and in the same beam as the output of the transmission power control device 328 , The output of the adder 336 becomes an analogue transmitter 338 for digital-to-analog conversion, conversion to the appropriate RF carrier frequency, further amplification and output to one or more antennas 340 to broadcast to the user terminals 124 . 126 delivered. The antennas 310 and 340 may be the same antennas, depending on the complexity and configuration of the system.
At least one gateway control processor 320 is with the receiver modules 324 , the transmitter modules 334 and the baseband circuit 322 coupled; these units can be physically separated. The control processor 320 provides command and control signals to effect such functions as, but not limited to, signal processing, timing signal generation, power control, handoff control, diversity combining, and system interface formation. In addition, the control processor arranges 320 PN spreading codes, orthogonal code sequences, and specific transmitters and receivers for use in user communications.
The control processor 320 Also controls the generation and performance of pilot, synchronization and paging channel signals and their coupling to the transmit power control device 328 , The pilot channel is simply a signal that is not data modulated, and may have a repeated non-changing pattern or frame structure type (pattern) or sound input to the transmit modulator 326 use. That is, the orthogonal function, the Walsh code used to form the channel for the pilot signal, generally has a constant value, such as only ones (1) or zeros (0), or a well-known one repeating pattern, such as a pattern of interspersed ones (1) and zeros (0). If, as is usually the case, the Walsh code used is a code of all zeros (0), this effectively results in only the PN spreading codes transmitted by the PN generator being transmitted 332 be applied.
While the control processor 320 can be directly coupled to the elements of a module, such as the transmitter module 324 or the receiving module 334 , each module generally includes a module-specific processor, such as a transmit processor 330 or a receiving processor 321 which controls the elements of this module. Thus, in a preferred embodiment, the control processor 320 with the send processor 330 and the receiving processor 321 coupled, as in 3 shown. In this way, a single control processor 320 control the operations of a large number of modules and resources more efficiently. The send processor 330 controls the generation of pilot, synchronization ons, paging signals and traffic channel signals and their signal power and their respective coupling to the power control device 328 , The receiver processor 321 controls search and PN spreading codes and the timing for the demodulation and monitoring of received power.
II. Transmission power control
4A illustrates details of a possible power control scheme of the user terminal transceiver (transceiver) 200 , A received signal becomes a demodulator 401 entered. In one embodiment, the demodulator 401 an A / D converter 402 , a pseudorandom noise (PN) correlator (PN = pseudorandom noise) 404 and a PN generator 406 on. The received signal is converted from analog to digital by an A / D converter 402 transformed. The digital signal coming from the A / D converter 402 is output becomes the correlator 404 where the signal undergoes a correlation process which compares the signal to a local reference for coincidence. In the illustrated embodiment, the correlator is 404 a PN correlator. Accordingly, the signal undergoes a correlation process with PN signals received from the PN generator 406 to be delivered. An edition 407 of the demodulator 401 is preferably a quantization element 408 delivered. The edition 409 of the quantization element 408 (or the output 407 if the quantization element 408 is not used) may have soft decision data corresponding to a confidence measure corresponding to a particular group of sampled signals to a particular orthogonal code of a set of orthogonal codes, generally using Walsh Codes have been set up. This edition 409 of the quantization element 408 (or the output 407 directly) becomes the user data decoder 410 supplied, the user data to the digital baseband circuit 224 provides what is described above. The decoder 410 uses maximum likelihood decoding techniques (estimated maximum likelihood techniques) to estimate estimated traffic channel data bits 411 to generate (also referred to as user data). The maximum likelihood decoding techniques can be improved by using an algorithm that is substantially similar to a Viterbi decoding algorithm, which is well known in the art.
It is considered that the components of the demodulator 401 and the quantization element 408 Components of the digital data receiver described above 216 are. Next, it is considered that components of the decoder 410 Components of the diversity combiner and decoder circuit 222 are as described above.
The quality of a user terminal, such as the user terminal 126 , received signal is measured by the user terminal. From this measurement, the fitness level of the signal power is determined, where poor signal quality is an indication of insufficient signal power. For example, a signal-to-noise ratio (SNR) estimation element 418 (SNR = Signal-to-Noise Ratio) the SNR or signal-to-noise ratio of the received signal based on the output 409 of the quantization element 408 (or the issue 407 directly). Alternatively or additionally, signal quality may be measured based on errors, such as based on frame errors. For example, an error detector 416 determine on a frame-by-frame basis whether an error has occurred or not. The error detector 416 may detect frame errors using well-known techniques, such as, but not limited to, using CRC bits or information.
The output of the SNR estimator 418 and / or the fault detector 416 becomes a performance command determinant 420 delivered. The power command determinant 420 determines whether or not the transmitter power (used to transmit the received signal) should be adjusted based on the quality of the received signal. In particular, the power command determining element 420 Generate power-up or power-down commands, which in turn are used to generate power-up or power-down request messages from the user terminal 126 for example to the gateway 122 be sent. Once at the gateway 122 are received, these power setting messages become the send processor 330 which in turn causes the transmit power control device 328 increases or decreases the power of the signals sent to the user terminal 126 be sent.
The power command determinant 420 may request such settings of the transmitted signal power based on measurements of the signal quality, such as based on SNR and / or frame errors. At a high level, the power command determiner compares 420 the signal quality measurements with signal quality thresholds. If a measured signal quality exceeds a corresponding threshold, the power command determination may be lement 420 request that the gateway 122 changes its transmitted signal power by a certain amount, either increased or decreased, if desired. In addition, if the measured signal quality does not exceed the threshold, the power command determiner may be added 420 request that the gateway 122 changes its transmitted signal power by a specific amount to save power and reduce, reduce or enlarge possible signal interference, if desired.
In particular, the power command determining element 420 Settings of the transmitter power of the gateway 122 based on the measured SNR of the received signal using the output 419 from the SNR estimator 418 determine. Accordingly, the power command determining element 420 determine that the transmission power of the gateway 122 should the SNR fall below a predetermined threshold or the transmit power should be reduced by a predetermined amount should the SNR be above the predetermined threshold.
Alternatively and / or additionally, the power command determination element 420 an FER of the received signal using the output from the error detector 416 determine. Accordingly, the power command determining element 420 determine that the transmission power of the gateway 122 should be increased by a predetermined amount when the FER is above a predetermined threshold (for example, 1%), or that the power should be reduced by a predetermined amount when the FER is below the predetermined threshold.
As will be discussed in more detail below, alternatively, the power command determining element may 420 Determine transmission power settings based on comparisons between a measured / estimated SNR and an SNR threshold, and may set the SNR threshold based on whether the FER falls below or exceeds a predetermined FER threshold.
is a calculation based on the number of frames,
that were received with errors, compared to frames that without
Errors were received. The SNR is a ratio of the sent useful
Signal, noise or unwanted signal. The application
of alternative measurements of signal quality, such as the bit error rate
(BER = Bit Error Rate) is also within the core and scope
of the present invention.
For the exemplary embodiments discussed, mention of adjustments (increases or decreases) in "transmitter power" or "transmit power" mean that the gateway 122 sets the amount of power it uses to send a signal (multiple signals) to a specific user terminal, such as the user terminal 126 , Additional details of the performance command determiner 420 will be discussed below.
III. Preferred embodiment
4B illustrates an alternative power control scheme according to a preferred embodiment of the present invention. This in 4B The illustrated power control scheme is similar to the power control scheme of FIG 4A in that it is a demodulator 401 , a quantization element 408 (preferably, but not necessarily) a user data decoder 410 , an error detector 416 and / or an SNR estimator 418 and a power command determination element 420 having. However, the embodiment of the differs 4B in a few important ways. First, the control scheme of the 4B also a distortion 412 and a virtual decoder 414 on. In addition, in this embodiment, the input to the SNR estimator is the output 413 of the distortion 412 instead of the exit 409 of the quantization element 408 (or the output 407 directly). Furthermore, the input is in the error detector 416 the exit 415 the virtual decoder 414 and not the exit 411 (User data) of the user data decoder 410 ,
It should be noted that the user data decoder 410 and the virtual decoder 414 physically separate components. Alternatively, the data decoder 410 and the virtual decoder 414 be a single decoder that is time division multiplexed to function as two decoders.
The distortion 412 distorts the output 409 of the quantization element 408 (or the output 407 directly), for example by adding pseudo noises to the output 409 , The effect of the distortion 412 is, the output or the output 409 of the quantization element 408 (or the output 407 ) to deteriorate. In the example where the output 409 from the quantization element 408 which are soft-decision data is the output 413 of the distortion 412 distorted soft-decision data corresponding to confidence levels that a particular group of sampled signals corresponds to a particular orthogonal code. Because of the distortion 412 are the confidence levels according to the issue 412 less / reduced compared to the output 409 ,
With reference to the virtual decoder 414 the term "virtual" is used because the output of the virtual decoder 414 are no user data that goes to digital baseband circuitry 224 to be delivered. The edition 411 from the user data decoder 410 is still becoming the digital baseband circuit 224 delivered in the same way as above in the meeting of the 4A described. However, it becomes a distorted output 415 the virtual decoder 414 instead of the issue 411 the user data decoder 410 (as in 4A ) used for power control. That is, the error detector 416 determines errors based on the output 415 of the virtual decoder instead of based on the output 411 , This causes the detected amount of error to be higher than if the error detector 416 Errors based on the actual user data 411 determined (as in 4A ).
In addition, a distorted output 413 to the SNR estimation element 418 delivered. Because the SNR estimator 418 the SNR of the distorted data 413 measures / estimates is the estimated SNR 419 which is the power command determining element 420 is lower / lower than the actual SNR of the output of the quantization element 408 (ie, the output 409 ).
In the embodiment of 4B determines the power command determination element 420 Whether or not to request a transmission power setting based on "wrong" signal quality measurements. That is, the power command determining element 420 makes determinations based on inputs indicating that the signal quality is worse than it actually is. For example, the SNR estimator becomes 418 estimate that the SNR is lower when the power control scheme of the 4B compared to when the power control scheme of 4A is used. Because the distorted data 413 to the virtual decoder 414 will be delivered in addition to the virtual decoder 414 make more frame errors than the user data decoder 410 , Accordingly, the error detector becomes 416 detect an increased number of errors when used in the power control scheme of FIG 4B In comparison, when used in the scheme of 4A is used. Therefore, the power command determining element becomes 420 if it is in the power scheme of the 4B earlier determine that a threshold has been exceeded than it would if it were in the power control scheme of the 4A is used (assuming that the same threshold is used in both schemes). This will cause the power command determinant 420 Power-up or power-down commands are generated before the signal quality thresholds actually for a non-distorted demodulated signal 409 (or 407 ) and / or user data 411 be achieved.
IV. Operation of the Leistungssteuerbestimmungselementes
The power command determinant 420
can perform the performance control features that are in the US patent application serial no. 09 / 164,384
which was filed on September 30, 1998, entitled "System and Method for Optimized Power Control", and in the US patent application serial no. 07 / 183.388
, filed Oct. 29, 1998, entitled "Variable Loop Gain in Double Loop Power Control Systems," both of which are owned by the assignee of the present invention. To complete, a description of how the present invention may be used in combination with features of the above-referenced patent applications is discussed in the review of 5
The 5 and 6 Fig. 10 are flowcharts showing the operation of the power command determining element 420 , the SNR estimation element 418 and the fault detector 416 in accordance with a preferred embodiment of the present invention. 5 maps the operation of an internal power control loop. The steps of 5 will likely be from the SNR estimator 418 and the power command determining element 420 executed. The function of the inner power control loop is to adjust the signal power coming from the gateway 122 is transmitted.
In the exemplary embodiments discussed above, the transmitted signal power is adjusted according to the level of signal power present at the transceiver 200 Will be received. In particular, the gateway sends 122 in these example embodiments, a signal (multiple signals) to the user terminal 126 , The signal is from the demodulator 401 demodulated and (preferably) by the quantization element 408 quantized. The quantized representation of the signal (ie, the output 409 ) then becomes a distortion 412 which outputs a distorted quantized representation of the signal, as discussed above. The edition 413 of the distortion 412 is intended as a distorted demodulated signal 413 be designated.
The method begins by measuring the power of the distorted signal 413 through the SNR estimator, as in step 502 shown. In a preferred embodiment, the SNR estimator measures 418 the signal-to-noise ratio (SNR) of the distorted signal 413 , In particular, the SNR estimator measures E b / N o , where E b is the energy per bit where N o is the noise density in units of power / cycle. Of course, other measurements of signal power may be used without departing from the scope of the present invention. In a preferred embodiment, the SNR is measured for each frame of received data.
In the communication system 100 For example, a predetermined SNR level, referred to as the "SNR threshold," is with the transceiver 200 associated. The SNR threshold represents the minimum SNR where signals from the transceiver or transceiver 200 should be received to ensure data quality. The SNR threshold can be selected according to methods well known in the art. One such method is to select an SNR that will hold data errors below a certain percentage, such as below one percent. In step 504 compares the power command determination element 420 the in step 502 measured SNR with the SNR threshold.
If the measured SNR is lower than the SNR threshold, then the power control determiner generates 420 a "power-up command" that causes a power-up message to go to the gateway 122 is sent, as in the step 506 shown. In response, the gateway increases 122 the transmitted signal power by a predetermined amount (for example, by 0.5 dB), which is referred to as "inner loop gain" or "inner loop gain".
If the measured SNR exceeds the SNR threshold, then the power control determiner generates 420 of the transceiver 200 a "power-down command" that causes a power-down command to go to the gateway 122 is sent, as in the step 508 shown. In response, the gateway reduces 122 the signal power by a certain amount (for example, 0.004 dB). In any case, the process starts again at the step 502 at.
discussed above, if another quality measurement function
as the SNR is used, which is in inverse proportion
changed to the level of performance,
such as a technique involving the presence of "error events" or error rates
measures or relies on the signal power in reverse relation
set to the extent
around which the measurement deviates from the threshold. That is, if
the measured value exceeds the threshold,
the signal power is increased, and if it is less than the threshold
is, the signal power is reduced.
6 depicts the operation of the outer power control loop (also referred to as the "outer loop") used in one embodiment of the present invention. The steps of 6 will probably be through the fault detector 416 and the power command determining element 420 executed. The function of the outer power control loop is the SNR threshold of the transceiver or transceiver 200 adjust. In a preferred embodiment, the SNR threshold is adjusted according to the quality of the received signal. In a preferred embodiment, the quality of the signal is considered not only with respect to the current frame, but also for a certain number of previous frames. In a preferred embodiment, the measure of signal quality used is also a measured FER. However, other measures of signal quality, such as parity checks, may be used without departing from the scope of the present invention.
Regarding 6 The procedure begins by determining whether the current frame contains distorted data 415 (also referred to as distorted decision data) is erroneous or not, as in the step 602 shown. The method then determines if there are errors in the current frame, as in the step 604 shown. If there are no errors in the current frame, as by the branch "No" from the step 604 then reduces the power command determining element 420 the SNR threshold by a predetermined amount, as in the step 606 shown. However, if there are errors in the current frame, as from the branch "yes" from the step 604 shown, then the process again checks the quality of the received signal, as in step 608 shown. In a preferred embodiment, the error history comprises a predetermined number of previous frames N. Of course, the error pattern may be otherwise selected without departing from the scope of the present invention. The error history is stored in memory (not shown). If any of the previous N frames contain an error, then the power command determiner decreases 420 the SNR threshold around the outer loop gain, as in step 606 shown.
However, if the previous N frames contain no errors, then the power command determiner increases 420 the SNR threshold, as in step 610 shown. In a preferred embodiment, two change values are used: one to reduce the SNR threshold and the other to increase the SNR threshold. The change value for reducing the SNR threshold is relatively small, so that the SNR threshold and, by the action of the inner loop, the transmitted signal power is gradually reduced to error-free environments. In contrast, the change value for increasing the SNR threshold is relatively large, so that the SNR threshold, and through the inner loop effect, increases the transmitted signal power rapidly in error prone environments.
The operation of the power control designation element 420 who in the description of the 5 and 6 can be discussed in the power control schemes of 4A and 4B be used. However, an advantage of using the schema is the 4B in that the necessary extent of increase of the SNR threshold (ie, the outer loop gain) in response to a frame error being detected when the power control scheme of the 4B is used less than if the schema of 4A is used. In addition, the extent of the decrease (decrease) of the SNR threshold, when the power control scheme of the 4B is used, be greater than if the power control scheme of 4A is used. Since the total transmission power roughly follows increases and decreases in the SNR threshold, the overall transmission power is reduced when the power control scheme of FIG 4B is used.
The power control schemes of 4A and 4B are described as if signals from the gateway 122 over the satellite 116 to the user terminal 126 be sent. That is, the power control schemes of 4A and 4B are described as if the in 4A and 4B shown components in the user terminal 126 located, and the transmission power of the gateway 122 is controlled. It should be noted that the same power control schemes can be used when the user terminal 126 Signals from the base station 112 Receives signals. The only difference is that the power command determinant 420 will determine if the power coming from the base station 112 used to send signals to the user terminal 126 to send, set or not, and instead, whether that from the gateway 122 used power should be set or not. It should also be noted that although the power control schemes discussed above are described as being from the user terminal 126 used, relatively identical schemes from the gateway 122 or from the base station 112 can be used to adjust the performance of a user terminal 126 used to send signals to the gateway 122 or to the base station 112 to send. That is, the components of the 4A and 4B For example, in the gateway 122 be located, and the currently controlled transmission power may be that of the user terminal 126 be when a signal (multiple signals) to the gateway 122 over the satellite 118 is (are) sent. In addition, the power control schemes of the 4A and 4B used to transmit the transmission power of the user terminal 126 adjust if there is a signal (multiple signals) to the base station 112 sends.
V. high-level operation of the present
7 FIG. 10 is a flowchart that greatly simplifies operation and depicts the high-level operation of a preferred embodiment of the present invention. The method begins by demodulating a received signal as in the step 702 shown. The demodulated signal is then in step 704 distorted. This can be done, for example, by adding noise to the demodulated signal. Next is in step 706 determines a signal quality measurement based on the distorted demodulated signal (rather than based on the non-demodulated signal). This signal quality measurement can be, for example, a measurement of the SNR or signal-to-noise ratio. Finally, in step 708 a setting of the transmission power based on the in step 706 specific signal quality measurement requested.
The step 708 can the steps 710 . 712 . 714 and 716 exhibit. In step 710 will be in the step 706 certain signal quality measurement compared to a threshold. In step 712 a determination is made as to whether the signal quality measurement exceeds the threshold. If the answer in step 712 yes, then an increase in transmission power (for example, +0.5 dB) is requested. If the answer in step 714 is no, then a reduction of the transmission power (for example -0.5 dB) is requested.
The threshold, in the steps 710 and 712 is preferably set based on a second measurement of signal quality, as discussed above. For example, the distorted demodulated signal may be decoded to produce distorted decision data. A measure of the frame error may then be determined based on the distorted decision data. The threshold, in the steps 710 and 712 is used, then the frame errors can be adjusted based on this measurement.
For the preferred embodiment, where in the steps 710 and 712 used thresholds, it should be noted that when the user terminal 126 the Leistungssteusche ma the 4B then the power control determiner 420 not the SNR threshold in the step 610 need to increase as much as they would if the user terminal 126 the scheme of 4A would use. In particular, assume that the power settings of the gateway 122 based on comparisons with a SNR threshold. If the user terminal 126 the power control scheme of 4A to the signal transmission power of the gateway 122 then the power command determiner may be 420 its SNR threshold by about 3 dB in response to receiving the SNR threshold increase command in step 610 need to increase to ensure that the FER (of the undistorted demodulated signal 409 or 407 ) does not fall below a threshold FER. If the same user terminal 126 (within the same wireless communication system and in the same place), in contrast, the power control scheme of 4B would need, then the performance command determiner needs 420 less increase in its SNR threshold, for example 0.5 dB, to ensure that the actual FER (undistorted demodulated signal 409 or 407 ) does not fall below the FER threshold. The transmitter power of the gateway 122 follows essentially changes in the SNR threshold. This is because, if the scheme of 4B is used, the SNR threshold is increased before the actual SNR (ie, the SNR of the demodulated signal 407 or 409 ) falls below the SNR threshold. Because the transmitter power of the gateway 122 essentially following the increases and decreases of the SNR threshold, this will result in the gateway 122 does not have to increase its performance by as much as it would if the user terminal 126 the scheme of 4A would use. The transmitter power of the gateway 122 essentially follows the changes in the SNR threshold because of the performance of the gateway 122 based on power-up (for example, +0.5 dB) and power-down requirements (for example, -0.5 dB) provided by the power command determinant 420 which in turn are based on comparisons with the SNR threshold.
For the performance scheme of 4A In addition, the amount of SNR threshold reduction in response to a power-down command should be relatively low, for example 0.001 dB, to ensure that the FER does not drop below the FER threshold. In contrast, the SNR threshold may be responsive to a power-down command using the performance scheme of 4B downgraded faster, for example by 0.004 dB. This is because the SNR threshold (and thus the gateway transmit power) is increased before the actual SNR (ie, the SNR of the demodulated signal 407 or 409 ) reaches the SNR threshold.
The exemplary graph of the 8A illustrates the SNR threshold over time when the user terminal 126 the power control scheme of 4A used. How out 8A seeing increases the power control voting element 420 the SNR threshold at time t 1 . For this example, the power control determiner increases 420 the SNR threshold by 3 dB in response to an SNR threshold zoom in step 610 Will be received. At times before time t 1 , for example, when no frame errors are detected, the power control determination element decreases 420 the SNR threshold in step 606 , For this example, it is assumed that the power control determinant 420 decreases the SNR threshold by 0.001 dB in response to a SNR Threshold Decrease command in step 606 Will be received. Alternatively, the power control determination element may independently reduce its SNR threshold with time until it receives an SNR threshold increase command at time t 1 .
Still referring to 8A The area under the sawtooth curve is broadly proportional to the total amount of power passing through the gateway 122 used to send a signal (multiple signals) to the user terminal 126 over a period of time to send, since the power that the gateway 122 used to send a signal (multiple signals), essentially following the SNR threshold. One purpose of the present invention is to reduce this total amount of power while maintaining a desired signal quality. Accordingly, a reduction in overall performance can be illustrated by a reduction in the area under the sawtooth-like curve.
The exemplary graph of the 8B illustrates the SNR threshold over time when the user terminal 126 the power control scheme of 4B used. How out 8B seeing increases the performance command determiner 420 the SNR threshold at times t 1 't 2 ' , t 3 ', etc. when, for example, a framing error is detected (and has not been detected in N previous frames). Increasing the SNR threshold in response to receiving an SNR threshold increase command in step 610 is only 0.5 dB compared to 3 dB in 8A , In addition, the SNR threshold becomes faster at a SNR threshold decrement command in step 606 downgrades what occurs when no framing error is detected (e.g. at times between t 1 'and t 2 ').
The graphs of the 8A and the 8B are approximately on the same scale net. That is, if you look at the 8A and 8B It can be seen that increases in the SNR threshold are much greater in response to receiving an SNR threshold increase command 8A as in 8B are (3 dB compared to 0.5 dB). In response to receiving an SNR Threshold Decrease command, the SNR threshold continues to become much less fast 8A as in 8B downgraded (0.001 dB compared to 0.004 dB). Accordingly, it can be seen that the slope of the lines, which decreases the SNR threshold in 8B represent about four times larger than the slope of the 8A is. Because the transmitter power of the gateway 122 Following essentially the changes in the SNR threshold, these two graphs show that the necessary amount of transmission power when the power control scheme of the 4A is used (which of the graph in 8A is much larger than the magnitude of the transmitter power required when the power control scheme of the 4B is used (which the curve representation in 8B corresponds). The use of the performance control scheme of the 4B Resources and reduces potential signal interference.
adaptive power control scheme as discussed above
which uses a double-loop configuration is based on both
the measurement of SNR as well as on the measurement of errors to the
Application of power-up or power-down commands. In
In a non-adaptive scheme, it is sufficient to detect whether
the measured SNR over
or below some fixed threshold. For adaptive techniques, however, must
the threshold itself according to the number of
detect detected errors (the so-called outer loop). While it
practically quite common
is to achieve a relatively high FER or frame error rate, such as
1%, are orders of magnitude
lower error rates not practical. The reason is
in a system that works with high SNR, and therefore lower
FER, the absence of errors causes the threshold to be progressive
is lowered until the SNR is sufficiently low, so that a
too high FER is reached, and then the threshold in their value again
is increased or promoted. This causes a change
between periods with very low FER and slow drift to one
too high FER. What is desired
is, is a steady operation at low FER. If the virtual
Decoder is set up so that it distorts the received signal,
so that both the SNR measurement and the FER are degraded,
and when the virtual decoder issues power control commands; in which
at the same time there is a parallel undistorted receiver that
outputs true demodulated / decoded data; can then be the virtual one
Decoders work at a normal low FER, like 1% during the
Decoder with a FER works by one or several orders of magnitude
Area where the invention can be used to advantage is
the application of newer coding / decoding techniques (e.g.
Turbo coding). In these cases
can be the relationship between SNR and BER or FER as a curve
be seen, which has a very steep slope. That is, if that
SNR is just a bit too high or too low, it may be the error rate
to a more significant size or
to change orders of magnitude. It
is very difficult to adaptive power control techniques (for example
with double loop) if such coding
is used because such techniques some variation of the
delivered SNR generate what changes the error rate around
orders of magnitude
can result. The above-disclosed application of the technique
With virtual decoder, the "virtual decoder" allows for a non-steep or less steep
Region of the curve, with less impact on the error rate, works,
Decoder in a steep region with a higher (not deteriorated)
SNR works. The operation of the virtual decoder in one not
steep part allows the SNR change
Another area where the invention can be used to great advantage is in cases where power control must be both low latency and low frame error rate. Two similar examples are the transmission of data, either terrestrial or satellite, for T-bearer devices and for Asynchronous Transfer Mode (ATM) traffic. The T-bearer may be a mixture of traffic going to / from a customer to / from their service provider, which traffic may be a mix of digitized voice, digital video conferencing, Internet, and file transfer traffic. In such an application, the default service is for a low error rate, and the protocols built into each end assume a low latency. Thus, a radio link that provides this type of service must have the same characteristics to carry the data. For the ATM service, it can be said that in the simplest case of voice or video data, these services do not actually require low error rates, because the coding / decoding techniques for such real-time services are usually designed to withstand a fairly high error rate, without any to require retransmission. However, each ATM packet (cell) contains not only payload or payload data that can use a high error rate, but also address information that requires a low error rate to prevent they are lost. In general, repeating packets in real-time services is not allowed or possible. Therefore, the use of the virtual decoder arrangement disclosed above allows for improved control of error rates for such services, with the ability to provide lower frame error rates as appropriate, and maintain low latency if needed.
previous description of the preferred embodiments is provided
to enable a professional
to carry out the present invention
or apply. The various modifications to these embodiments
will be readily apparent to those skilled in the art and the general ones
here defined principles can
to other embodiments
be applied without the application of inventive step. Consequently
the present invention is not intended to the embodiments shown here